UC-NRLI 


SB    75 


Quantitative  Relationships  of  Carbon, 
Phosphorus,  and  Nitrogen  in  Soils 


PRESENTED  TO  THE 


FACULTY  OF  THE  UNIVERSITY  OF  ILLINOIS 


URBANA,  ILLINOIS,  U.  S.  A. 


•    AS  A 


Thesis  for  the  Degree  of  Doctor  of  Philosophy 

JUNE,   1909 
BY 

%L.  *"/ 

ROBERT  STEWART,  B.  S. 


PUBLISHED  BY 

THE  UNIVERSITY  OF  ILLINOIS 

AGRICULTURAL  EXPERIMENT  STATION 

AS  BULLETIN  No.  145 


UNIVERSITY  OF  ILLINOIS 


Agricultural  Experiment  Station 


BULLETIN  NO.  145 


QUANTITATIVE  RELATIONSHIPS  OF 

CARBON,  PHOSPHORUS,  AND 

NITROGEN  IN  SOILS 


BY  ROBERT  STEWART 


URBANA,  ILLINOIS,  APRIL,  1910 


NOTE 

Robert  Stewart  was  born  in  American  Fork,  Utah,  August  16, 
1877.  He  secured  his  common  school  education  in  the  public 
schools  of  Utah.  In  the  fall  of  1896  he  .entered  the  preparatory 
department  of  the  Agricultural  College  of  Utah.  He  graduated 
from  this  institution  in  June,  1902,  with  the  degree  of  Bachelor  of 
Science.  He  immediately  received  an  appointment  as  assistant 
chemist  in  the  Utah  Experiment  Station.  While  holding  this  po- 
sition, during  t^e  years  1902-03,  1903-04,  he  took  graduate  stu- 
dent work  in  the  college.  During  the  school  year  1904-05  he  was 
a  member  of  the  Graduate  School  of  the  University  of  Chicago 
where  he  studied  chemistry  under  the  direction  of  Doctor  Nef.  In 
1905  he  was  appointed  assistant  professor  of  chemistry  in  the  Utah 
College  and  while  holding  this  position,  during  the  years  1905-06, 
1906-07,  1907-08,  he  continued  his  graduate  student  work.  Dur- 
ing the  summer  of  1906  he  was  a  member  of  the  Graduate  School 
of  Agriculture  held  at  the  University  of  Illinois.  In  June,  1908, 
he  was  appointed  professor  of  chemistry  in  the  Utah  College  and 
was  granted  a  leave  of  absence  to  carry  on  graduate  work  at  the 
University  of  Illinois. 

He  is  the  senior  author  of  Bulletin  103,  "Milling  Qualities  of 
Utah  Wheat,"  and  Bulletin  106,  "A  Study  of  the  Influence  of  Irri- 
gation Waters  upon  the  Movement  and  Production  of  Nitrates  in 
the  Soil,"  which  has  been  accepted  for  publication  by  the  Utah  Ex- 
periment Station. 

During  the  school  year  1908-09  he  held  a  fellowship  in  agron- 
omy in  the  University  of  Illinois.  He  is  a  member  of  the  Illinois 
chapter  of  Sigma  Xa  ,and  also.  ae  chftiter  member  of  the  Illinois 
chapter  of  the  Ametfieah  Socjrety: -6! Agronomy. 


QUANTITATIVE  RELATIONSHIPS  OF 
CARBON,  PHOSPHORUS  AND 
NITROGEN  IN  SOILS* 


BY  ROBERT  STEWART 


(A)    HISTORICAL  RfiSUMfi 

The  literature  on  carbon,  nitrogen  and  phosphorus  in  soils^  is 
voluminous.  The  resume  given  herewith  by  no  means  attempts  to 
include  all  that  pertains  to  these  elements  in  the  soil,  but  it  is  con- 
fidently believed  that  it  fairly  represents  the  literature  pertaining 
to  this  particular  phase  of  the  subject. 

i.  CARBON  IN  SOILS 

Carbon  may  exist  in  soils  as  inorganic  and  organic  carbon.  The 
agricultural  value  of  organic  carbon,  or  organic  matter,  of  soils 
has  long  been  recognized  by  the  practical  husbandman,  and  the 
scientific  man  early  recognized  its  value  when  the  applications  of 
science  were  made  to  agricultural  problems. 

Mulder  (i)  in  1844,  made  an  elaborate  study  of  the  organic 
matter  of  the  soil,  and  seems  to  have  been  the  first  one  to  suggest 
that  it  consisted  of  other  elements  than  carbon,  hydrogen  and 
oxygen.  He  separated  the  organic  matter  into  various  supposed 
pure  organic  compounds  of  an  acid  nature,  which  were  analyzed 
and  studied  by  the  usual  organic  method. 

Wolff  (2)  determined  the  organic  matter  of  the  soil  by  calcu- 
lation, by  use  of  the  factors  1.724  or  0.471  :  he  multiplied  the  or- 
ganic carbon  by  the  former  factor,  or  the  total  organic  carbon 
dioxid  by  the  latter.  The  factors  were  derived  from  the  concep- 
tion that  "humus"  contained  58  percent  carbon. 

Detmer  (9)  attempted  to  isolate  "pure"  humic  acid  from  the 
soil  and  to  study  its  properties.  He  obtained  a  fairly  pure  product 
which  he  studied  and  submitted  to  analysis. 

A  little  later  Grandeau  (10)  developed  his  well  known  method 
for  determining  the  matiere  noire  of  soils,  which  he  regarded  as 
of  great  importance.  He  stated  that  soils  owed  their  color  and 

*Submitted  to  the  Faculty  of  the  Graduate  School  of  the  University  of  Illinois 'in  partial 
fulfillment  of  the  requirements  for  the  degree  of  Doctor  of  Philosophy,  June,  1909. 

91 

254143 


92 


BULLETIN  No.  145 


[April, 


probably  their  fertility  to  its  presence  since  it  held  in  combination, 
phosphorus,  nitrogen,  and  certain  mineral  elements. 

Deherain  (22)  determined  the  carbon  content  of  soils  from 
plots  which  had  received  different  treatment.  He  found  that  the 
soils  from  the  plots  which  had  not  been  manured  had  lost  over 
50  percent  of  their  carbon. 

Kostytschiff  (24)  .studied  the  humus  obtained  from  substances 
of  known  origin  and  which  were  'converted  into  humus  under  con- 
trolled conditions.  He  learned  that  even  with  the  albuminous  sub- 
stances the  carbon  was  lost  more  rapidly  than  the  nitrogen,  hence 
the  ratio  of  carbon  to  nitrogen  would  be  narrower  in  the  resulting 
humus  than  in  the  original  material. 

Berthelot  and  Andre  (31)  found  that  67.1  percent  of  the  total 
carbon  in  soils  was  soluble  in  dilute  alkalis  .but  that  over  one-half 
of  this  soluble  carbon,  or  40  percent  of  the  total  carbon;  was  not 
precipitated  from  the  alkalin  solution  by  the  addition  of  an  acid. 

Snyder  (37)  reported  the  results  obtained  by  a  study  of  the 
production  and  analysis  of  the  humus  obtained  from  such  sub- 
stanees  as  cow  manure,  clover,  meat  scrap,  etc.,  etc.,  which  were 
converted  into  humus  under  known  conditions.  The  carbon 
content  of  the  humus  varied  from  41.95  percent  in  case  of  the  hu- 
mus produced  from  cow  manure  to  57.84  percent  in  case  of  the 
humus  produced  from  cane  sugar. 

Hess  (45)  studied  the  effect  of  different  systems  of  treatment 
on  the  humus  of  the  soil.  He  found  that  the  ratios  of  carbon  to 
nitrogen  and  nitrogen  to  humus  were  not  materially  effected  by  the 
treatment  applied. 

Andre  (47)  studied  the  action  of  potassium  hydroxid  on  the 
carbon  compounds  of  the  soil,  mould,  compost  and  peat.  He  de- 
termined the  insoluble  and  soluble  carbon :  the  latter  he  separated 
into  two  classes;  the  portion  precipitated  from  alkalin  solution  by 
the  addition  of  an  acid,  and  the  portion  remaining  in  solution.  The 
results  obtained  are  expressed  in  Table  i. 

TABLE  1. — PERCENTAGE  OF  SOLUBLE  AND  INSOLUBLE  CARBON  AND  RATIO 
OF  CARBON  TO  NITROGEN 


Peat 

Compost 

Soil 

Mould 

Ratio 
of 

C/N 

Percent 
carbon 
of 
total 

Ratio 
of 

C/N 

Percent 
carbon 
of 
total 

Ratio 
of 

C/N 

Percent 
carbon 
of 
total 

Ratio 
of 

C/N 

Percent 
carbon 
of 
total 

Insoluble  portion 

147.6 

24.5 

84.4 

4).0 

82.4 

35.4 

40.4 

41.8 

Sol- 
uble 
por- 
tion 

a.  Precipitated 
by  acids 

26.9 

44.8 

16.6 

23.0 

27.1 

36.6 

10.8 

18.7 

b.  Not  precipi- 
ta'ed  by  acids 

17.7 

30.7 

9.  8 

37.0 

16.7 

28.0 

10.1 

39.5 

ip/o]  CARBON,  PHOSPHORUS  AND  NITROGEN  IN  SOILS  93 

The  ratio  of  carbon  to  nitrogen  in  the  original  material  was: 
peat  22.7;  compost  15.0;  soil  24.7  and  mould  12.8.  He  concluded 
that  the  more  insoluble  the  compound  the  wider  was  the  carbon- 
nitrogen  ratio.  The  potassium  hydroxid  showed  a  tendency  to  dis- 
solve the  compounds  rich  in  nitrogen. 

Pagnoul  (51)  found  no  fixed  relation  between  the  carbon  and 
nitrogen  of  the  soil  but  apparently  the  carbon,  nitrogen,  and  humus 
varied  in  the  same  direction,  altho  irregularly. 

Rimbach  (53)  concluded  that,  since  the  matiere  noire  was 
readily  nitrified  it  was  the  direct  source  of  the  nitrates  of  the  soil 
and  thus  the  insoluble  carbon  was  of  insignificant  value. 

Frear  and  Hess  (54)  found  that  lime  caused  a  more  rapid  loss 
of  carbon  than  of  nitrogen  in  manured  land,  but  the  reverse  in  un- 
manured  land. 

Dyer  (55)  studied  the  carbon  and  nitrogen  content  and  the  re- 
lationship between  carbon  and  nitrogen  in  the  soil  taken  from  22 
different  plots  of  the  Rothamsted  experiment  fields.  These  data 
are  furnished  for  each  individual  Q-inch  section  to  a  depth  of  90 
inches. 

The  carbon  and  nitrogen  contents  of  the  higher  depths  were 
higher  than  those  of  the  lower  depths  and  the  ratio  of  carbon  to 
nitrogen  is  wider  in  the  former.  At  the  fifth  to  sixth  depth  the 
carbon  and  nitrogen  contents  seem  to  become  fixed  quantities  and 
are  apparently  those  derived  from  the  original  matter  out  of  which 
the  soil  was  formed. 

A  study  of  various  clays  and  other  material  taken  from  great 
depths  seemed  to  indicate  that  a  nitrogen  content  of  .04  percent 
was  indigenous  to  the  subsoil  of  the  Rothamsted  station. 

Cameron  and  Breazeale  (61)  investigated  the  three  general 
methods  for  determining  the  carbon  content  of  the  soil :  namely, 
the  "loss  on  ignition"  method,  the  humus  method  and  two  forms 
of  a  combustion  method.  They  concluded  that  the  first  two  meth- 
ods were  unreliable :  the  first,  because  there  was  no  apparent  re- 
lationship existing  between  the  results  obtained  and  the  true  carbon 
content ;  the  second,  since  it  makes  no  pretense  of  giving  the  total 
carbon  in  the  soil. 

It  is  interesting  to  note  that  they  reported  that  the  ammoniacal 
extract  contained  so  much  suspended  material  that  it  was  found 
undesirable  to  work  with,  until  it  was  passed  through  a  Chamber- 
land-Pasteur  filter,  when  a  perfectly  clear  solution  was  obtained. 

Konig  (67)  recently  studied  the  influence  of  hydrogen  peroxid 
on  the  organic  matter  of  the  soil.  He  found  that  it  consisted  of 
two  parts,  one  easily  oxidized  by  hydrogen  peroxid,  the  other  not 
oxidized  by  this  reagent. 


94  BULLETIN  No.  145  [April, 

Hopkins  and  Pettit  (68)  reported  the  total  carbon,  nitrogen 
and  phosphorus  contents  of  a  great  number  of  samples  of  the  soils 
of  Illinois.  This  work  is,  thus,  made  the  basis  of  calculating  the 
relationship  of  carbon,  nitrogen  and  phosphorus  reported  in  part 
(B)  of  this  thesis. 

2.    NITROGEN  IN  SOILS 

The  nitrogen  in  soils  exists  chiefly  as  organic  nitrogen  with  a 
very  small  amount  of  inorganic  nitrogen.  The  organic  nitrogen 
may  exist  in  some  known  and  probably  some  unknown  forms. 

Mulder  (i)  believed  the  nitrogen,  found  in  the  humus,  to  be 
associated  with  the  organic  matter  in  the  form  of  the  ammoniacal 
salts  of  the  various  organic  acids  obtained  by  him. 

Miiller  (4)  thought  he  detected  a  tendency  for  the  nitrogen  to 
vary  inversely  as  the  carbon. 

Detmer  (9)  believed  that  the  nitrogen  formed  a  definite  com- 
pound with  the  organic  carbon  of  the  soil  since  the  nitrogen  could 
be  liberated  only  with  great  difficulty  and  by  the  use  of  the  most 
drastic  chemical  agents. 

Simon  (n)  believed  that  the  organic  matter  of  the  soil  pos- 
sessed the  property  of  absorbing  the  free  nitrogen  of  the  at- 
mosphere and  of  converting  it  into  ammonia  which  in  turn  united 
with  the  organic  acids  in  the  form  of  their  ammoniacal  salts.  Sos- 
tegni  (19)  a  little  later  discussed  trie  work  of  Simon  and  reported 
a  series  of  experiments  to  prove  that  Simon's  assumption  was  un- 
tenable. 

Berthelot  (19),  in  1886,  reported  the  carbon  and  nitrogen  con- 
tents of  calcareous  clayey  soil,  originally  very  deficient  in  organic 
carbon  and  nitrogen  but  which  was  gradually  increasing  in  carbon 
and  nitrogen  content  owing  to  the  action  of  diatoms. 

Berthelot  and  Andre  (20,  74,  75,  76)  later  carried  on  a  series 
of  experiments  for  the  purpose  of  separating  the  organic  nitro- 
genous material  into  its  various  compounds.  They  reported  the 
amount  of  total,  nitric,  amido  and  ammoniacal  nitrogen  present  in 
the  soil. 

Eggertz  (21)  differed  very  materially  from  Mulder.  He  con- 
cluded that  Mulder's  contention,  that  the  nitrogen  associated  with 
the  organic  matter  of  the  soil  existed  only  as  the  ammoniacal  salts 
of  the  various  organic  acids,  was  untenable.  If  the  nitrogen  ex- 
isted simply  as  the  ammoniacal  salt  of  the  humic  acid,  treatment 
with  hydrochloric  acid  should  liberate  all  the  nitrogen  as  ammonia, 
which,  experimental  evidence  showed,  was  not  the  case. 

Furthermore  artificial  humic  acid,  treated  with  ammonia,  did 
form  ammonium  humate  which,  however,  was  readily  decomposed 


ip/o]  CARBON,  PHOSPHORUS  AND  NITROGEN  IN  SOILS  95 

by  treatment  with  a  mineral  acid;  yet,  if  this  artificial  liumic  acid 
be  heated  in  a  current  of  ammonia  gas,  combination  took  place  and 
the  resulting  compound  could  not  be  decomposed  by  treatment 
with  mineral  acids.  He,  therefore,  concluded  that  the  nitrogen 
formed  an  integral  part  of  the  humic  acid  radical. 

Berthelot  and  Andre  (26)  studied  artificial  humic  acid  pre- 
pared out  of  sugar.  This  acid  formed  salts  with  various  bases, 
which  were  easily  decomposed  again  by  treatment  with  an  acid, 
except  in  the  case  of  the  ammonium  sali,  the  nitrogen  of  which 
could  not  be  entirely  liberated  by  this  treatment.  They  concluded 
that  the  nitrogen  in  part  at  least,  formed  an  integral  part  of  the 
humic  acid  radical. 

Hilgard  arid  Jaffa  (3o),4n  1892,  propounded  their  well  known 
view  regarding  the  importance  of  the  nitrogen  associated  with  the 
extracted  matiere  noire. 

Berthelot  and  Andre  (31)  regarded  the  organic  matter  of  the 
soil  as  of  great  importance  since  it  prevented  the  loss  of  nitrogen 
thru  drainage  since  the  nitrogen  was  held  in  insoluble  combination 
in  the  organic  matter. 

Fulmer  (38)  determined  the  humic  nitrogen  in  53  samples  of 
Washington  soil  and  attempted  to  work  out  the  relationship  be- 
tween carbon  and  nitrogen  by  means  of  the  formula  c=  ^~, 
where  c=  the  percentage  of  nitrogen  in  the  matiere  noire;  b= 
the  percentage  of  the  total  soil  nitrogen;  a=  the  percentage  of 
humus.  By  means  of  this  formula  the  53  samples  of  soil  were 
separated  into  three  classes;  the  first  class  contained  19  samples  in 
which  the  variation  in  the  humic  nitrogen  calculated  by  means  of 
the  formula  was  within  one  percent  of  the  analytical  result;  the 
second  class  contained  10  samples  and  the  variation  was  from  one 
to  two  percent ;  the  third  class  contained  24  samples  and  the  varia- 
tion was  anywhere  over  two  percent.  These  results  furnished  good 
evidence  that  no  one  given  relation  would  hold  for  all  soils. 

Wheeler  (48)  found  that  lime  or  gypsum  caused  a  decrease  in 
the  amount  of  humus  but  that  the  percentage  of  humic  nitrogen 
was  increased.  Similar  results  were  obtained  by  Frear  and  Hess 
(54)  on  manured  land. 

Dojarenko  (56)  recently  studied  the  "humic"  nitrogen  of  soils. 
He  determined  the  total,  humic,  amid,  ammoniacal  and  amido  ni- 
trogen in  seven  samples  of  black  Russian  soils.  The  results  are 
reported  in  Table  2. 


96 


BULLETIN  No.  145 


[April, 


TABLE  2.— PERCENTAGE  OF  TOTAL  HUMIC,  AMIDO,  AMID  AND  AMMONIACAL 

NITROGEN  IN  HUMUS 


Percent  in  dry  substance 

Percent  of  total  quantity 
of  nitrogen 

No. 

Total 
humic 
nitrogen 

Atnido 
nitrogen 

Amid 
nitrogen 

Ammo- 
niacal 
nitrogen 

Amido 
nitrogen 

Amid 
nitrogen 

Ammo- 
niac^! 
nitrogen 

1 

2 
3 
4 
5 
6 
7 

2.735 
3.38 
2.64 
3.33 
4.58 
3.65 
4.02 

1.34 
1.81 
1.30 
2.34 
1.01 
1.26 
1.96 

0.31 
0.41 
0.29 
0.32 
0.48 
0.27 
0.22 

0.04 
0.08 
0.02 
0.03 
0.06 
0.07 
0.03 

49.09 

53.55 
49.20 
70.27 
22.01 
34.52 
48.75 

11.38 
12.13 
10.99 
9.61 
10.46 
7.40 
5.47 

1.46 
2.36 
0.80 
0.90 
1.31 
1.90 
0.78 

This  did  not  account  for  all  of  the  nitrogen  present  and  so  the 
question  arises  in  what  form  does  the  remainder  exist? 

D'Utra  (70)  found  that  the  humic  nitrogen  showed  wide  vari- 
ations. 

Hilgard  (71)  reported  the  average  humic  nitrogen  of  466 
samples  of  soil  from  the  humid  regions  as  5.45  percent,  while  the 
average  of  313  samples  of  soil  from  the  arid  section  was  15.87 
percent.  Later  (73)  he  found  that  the  average  humic  nitrogen  for 
696  samples  of  humid  soil  was  5.00  percent,  while  that  of  573 
samples  of  arid  soil  was  15.23  percent.  It  must  be  remembered, 
however,  that  the  total  quantity  of  nitrogen  of  the  two  regions  is 
in  the  inverse  order.  The  total  nitrogen  of  the  uplands  and  low- 
lands of  California  for  example,  is  o.ioi  percent  and  o.ioi  per- 
cent respectively,  while  the  total  nitrogen  of  the  ordinary  brown 
silt  loam  soils  of  the  corn  belt  in  Illinois  varies  from  0.218  percent 
to  0.337  percent. 

3.   PHOSPHORUS  IN  SOILS 

The  phosphorus  of  the  soil  may  exist  in  the  inorganic  and 
organic  condition.  The  greater  part  is  in  the  inorganic  form  with 
an  unknown  amount  in  the  organic  state.  The  form  and  amount 
of  the  organic  phosphorus  is  uncertain,  and,  indeed  it  has  been 
questioned,  especially  during  recent  years,  whether  or  not  organic 
phosphorus  occurred  in  the  soil  to  any  appreciable  extent. 

Mulder  (i),  as  early  as  1844,  noted  that  the  organic  material 
was  not  readily  freed  from  phosphorus. 

The  work  of  Thenard,  Schutzenber  (5,  6,  7)  showed  that  union 
may  take  place  between  various  forms  of  artificial  humus  and  phos- 
phates under  certain  conditions  and  indicated  that  combination  may 
possibly  take  place  in  the  soil  between  organic  carbon  and  inorganic 
phosphorus. 

Detmer  (9)  in  the  preparation  of  his  "pure  humic"  acid,  noted 


jpio]  CARBON,  PHOSPHORUS  AND  NITROGEN  IN  SOILS  97 

that  the  material  could  be  freed  from  phosphorus  only  with  great 
difficulty. 

Grandeau  (10)  regarded  the  phosphorus  associated  with  the 
extracted  matiere  noire  as  being  of  the  greatest  importance,  and, 
was  probably  in  special  combination  with  the  organic  matter.  He 
regarded  it  as  an  index  of  the  fertility  of.  the  soil. 

Simon  ( 1 1 )  believed  that  he  had  demonstrated  that  union  took 
place  between  organic  matter  and  phosphates.  When  freshly  pre- 
cipitated humic  acid  was  suspended  in  water  and  digested  with 
calcium  phosphate  and  then  filtered,  the  filtrate  showed  an  excess 
of  phosphoric  acid:  this  excess,  he  concluded  must  be  in  union 
with  the  organic  matter  in  solution.  He  thought  that  a  double  com- 
pound of  ammonia  and  phosphorus  existed  in  the  soil. 

Schultz  (12)  showed  that  the  addition  of  humus  to  "Basalt- 
boden"  increased  the  absorption  ability  of  the  soil  for  phosphates. 

Eichhorn  (13)  repeated  some  of  Simon's  work  and  concluded 
that  organic  combination  did  not  take  place  as  indicated  by  Simon 
but  that  the  humus  had  decomposed  the  tri-calcium  phosphate  with 
the  formation  of  acid  phosphate. 

Pitsch  (14)  determined  the  solubility  of  the  various  mineral 
phosphates,  including  iron  and  aluminium  phosphates,  in  a  solu- 
tion of  ammonium  humate  itself.  He  concluded,  that,  since  this 
solution  exerted  a  solvent  action  on  mineral  phosphates,  the  am- 
monia extract  of  the  soil  contained  phosphorus,  other  than  that 
originally  associated  with  the  organic  matter  in  the  soil  and  prob- 
ably part,  at  least,  of  the  ammonia  soluble  phosphorus  was  derived 
from  the  iron  and  aluminium  phosphates. 

M.  P.  DeGasparin  (15)  found  in  calcareous  clay  soil  five  per- 
cent of  the  total  phosphorus  in  organic  combination.  He  noted, 
furthermore,  that  the  mosses  and  lichens  contained  from  5  to  6 
times  as  much  phosphorus  as  the  rocks  on  which  they  grew ;  the 
soil  formed  therefore,  from  the  debris  of  these  plants  should  be 
relatively  richer  in  phosphorus  and  should  have  a  part  of  its  phos- 
phorus in  combination  with  carbon  in  the  organic  material. 

Eggertz  (21)  found  that  the  ammoniacal  extract  of  the  soil, 
when  treated  with  an  acid,  formed  a  precipitate  of  organic  matter 
which  always  contained  phosphorus.  He  concluded,  therefore,  that 
part  of  the  phosphorus  of  the  soil  was  united  to  the  carbon  in  or- 
ganic combination. 

Later,  Eggertz  and  Nilson  demonstrated  that  the  amount  of 
phosphorus  soluble  in  dilute  mineral  acids  showed  a  marked  in- 
crease after  ignition  of  the  soil.  Ignition  rendered  10  times  as 
much  phosphorus  soluble  in  2  percent  hydrochloric  acid.  They 
attributed  this  to  the  destruction  of  the  organic  matter  which  had 
held  the  phosphorus  in  combination  which  would  not  yield  up  its 
phosphorus  to  acids. 


93  BULLETIN  No.  145  [April, 

Van  Bemmelen  (23)  believed  that  the  iron,  calcium,  silica, 
phosphoric  acid,  etc.,  found  in- the  ash  of  the  matiere  noire  by  Eg- 
gertz,  were  not  originally  chemically  combined  to  carbon  in  the 
organic  matter  of  the  soil  but  were  absorbed  by  the  precipitated 
gelatinous  matiere  noire.  According  to  Van  Bemmelen  the  phos- 
phorus existed  in  the  soil  principally  as  calcium  phosphate  with  a 
very  small  quantity  occurring  in  the  absorbed  state  in  the  form  of 
a  colloidal  en  Humate-Silicat-Komple.i". 

Two  questions  seemed  to  be  of  paramount  importance  to  Wik- 
lund  (25)  regarding  the  work  of  Eggertz:  first,  was  the  amount 
of  the  ammonia-soluble  phosphorus  obtained  from  different  soils 
constant?  Second,  did  the  phosphorus  exist  in  the  mullkorpers 
(matiere  noire  of  Grandeau)  in  chemical  combination  with  carbon, 
or  simply  as  absorbed  phosphorus?  He  concluded  that  there  was 
a  tendency  for  the  ammonia-soluble  phosphorus  to  be  constant  in 
different  soils.  He  showed,  further,  that  one  digestion  with  12 
percent  hydrochloric  acid  did  not  completely  remove  all  of  the 
acid  soluble  phosphorus,  but  a  second  and  even  a  third  digestion 
still  removed  some  phosphorus.  Now,  he  reasoned,  if  the  phos- 
phorus removed  by  the  second  and  third  digestion  was  simply  ex- 
tracted from  the  absorbed  phosphorus,  extraction  of  the  soil  with 
ammonia  after  the  first  digestion  with  hydrochloric  acid,  should 
yield  a  solution  of  matiere  noire  containing  a  higher  phosphorus 
content  than  when  the  soil  was  completely  extracted  with  the  hy- 
drochloric acid.  Such,  however,  was  not  the  case,  therefore,  the 
phosphorus  did  not  exist  as  absorbed  phosphorus  and  must  be  in 
combination  with  carbon  in  the  organic  matter. 

Snyder  (34)  noted  that  some  phosphorus,  iron,  etc.,  were  ex- 
tracted with  the  matiere  noire  but  he  did  not  seem  to  think  at  this 
time  that  there  was  any  evidence  of  combination  with  carbon. 
About  the  same  time  he  observed  the  rapid  loss  of  phosphorus  as- 
sociated with  the  humus  in  continuous  cultivated  soil. 

According  to  Berthelot  and  Andre  (27)  phosphorus  may  be 
found  in  the  soil  (a)  in  inorganic  or  mineral  phosphates,  (b)  in 
organic  ethers  and  (c)  in  organic  or  mineral  compounds  not  read- 
ily decomposed. 

Schmoeger  (29)  reviewed  the  rival  claims  of  Eggertz  and  Nil- 
son,  and  Wiklund  on  the  one  hand,  and  Van  Bemmelen  on  the 
other,  regarding  the  phenomenon  of  ignition  rendering  the  phos- 
phorus of  peaty  soil  more  readily  soluble  in  acids. 

It  seemed  possible  to  Schmoeger  that  the  soil  might  possess 
such  a  tenacious  absorbent  power  for  phosphorus  that  it  would  not 
yield  up  its  phosphorus  to  acid  treatment  before  ignition.  But  he 
deduced  experimental  evidence  to  show  that  such  was  not  the  case. 


jpio]  CARBON,  PHOSPHORUS  AND  NITROGEN  IN  SOILS  99 

Digestion  of  the  soil  itself  and  also  the  extracted  matlere  noire 
with  a  solution  of  potassium  hydrogen  phosphate  failed  to  add  any 
phosphorus  which  was  not  again  recovered  by  treatment  with 
hydrochloric  acid.  This  was  conclusive  evidence  to  Schmoeger 
that  the  phosphorus  did  not  exist  as  absorbed  phosphorus  and  must, 
therefore,  exist  in  organic  combination.  Two  possibilities  sug- 
gested themselves  to  Schmoeger:  first,  the  phosphorus  existed  in 
the  form  of  lecithin ;  second,  it  existed  as  nuclein.  Lecithin  was 
found  to  be  present  only  in  traces.  The  characteristic  property  of 
nuclein  to  "split-off"  its  phosphorus  in  the  form  of  phosphoric 
acid,  when  heated,  under  pressure  in  the  presence  of  water,  to  a 
temperature  of  I5o°-i6o°  was  utilized  by  Schmoeger.  The  soil 
under  examination,  treated  in  this  way,  yielded  as  much  soluble 
phosphorus  as  did  the  ignited  soil.  This  experimental  evidence 
led  him  to  conclude  that  nuclein  or  some  closely  allied  bodies  were 
present  in  the  soil. 

Later  Schmoeger  (39)  confirmed  his  previous  work  and  pro- 
duced additional  evidence  in  favor  of  his  view  that  nuclein  or  simi- 
lar bodies  existed  in  the  soil.  Table  3  shows  some  of  the  results 
obtained. 

TABLE  3. — PERCENTAGE  OF  SULFURIC  ACID  AND  PHOSPHORUS  SOLUBLE  IN 

DILUTE  ACID 


Percent 

Sulfuric  Acid 

Phosphorus 

Soil  in  original  state       

0.122 
0290 
0.939 

0.043 
0.083 
0.095 

Evaporated  soil 

Ignited  soil  

Since  sulfur  is  regarded  by  many  authors  as  being  a  constitu- 
ent of  plant  nuclein,  the  increased  solubility  of  this  substance  to- 
gether with  the  phosphorus  when  the  soil  was  treated  as  indicated 
alx>ve,  was  regarded  as  evidence  in  favor  of  his  assumption. 

In  a  later  article  (40)  he  showed,  by  similar  treatment,  that 
analogous  bodies  existed  in  the  moor  grass  out  of  which  the  moor 
soil  was  formed.  This  was  regarded  as  additional  evidence  in  favor 
of  his  view. 

Tacke  (33)  observed  that  the  drying  out  of  soil  rendered  the 
phosphorus  available.  There  were  three  possible  explanations  sug- 
gested to  him :  first,  the  phosphorus  existed  in  the  soil  in  organic 
combination  which  was  destroyed  by  the  process  of  drying;  second, 
it  existed  in  the  soil  in  the  colloidal  form  as  suggested  by  Van  Bem- 
melen;  third,  the  drying  out  of  the  soil  gave  rise  to  substances  of 
a  strong  acid  nature  which  acted  upon  the  insoluble  phosphorus 
compounds  rendering  the  phosphorus  soluble. 


100  BULLETIN  No.  145  [April, 

In  a  later  article  (42)  he  showed  that  very  little  water  soluble 
phosphorous  existed  in  the  soil  under  consideration,  but  that  dry- 
ing1 at  7o°-8o°  rendered  over  50  percent  of  the  total  phosphorus 
soluble  in  water. 

Snyder  (36)  reported  results  of  a  confirmative  nature  regard- 
ing the  phosphorus  associated  with  the  humus  in  virgin  and  cul- 
tivated soils. 

L,a.ter  he  (37,41)  studied  the  product  obtained  by  the  conver- 
sion of  known  substances,  under  known  condition,  into  humus. 
The  ash  of  the  mailer e  noire  obtained  from  this  material  contained 
phosphorus,  among  other  substances,  and  according  to  Snyder : 
"There  is  every  indication  that  these  elements  are  in  organic  com- 
bination with  the  carbon,  hydrogen  and  oxygen  of  the  humus." 
As  regards  the  question  whether  or  not  the  humus  united  with  the 
inorganic  phosphorus  of  the  soil,  he  concluded  that  his  experi- 
mental evidence  showed  that  such  union  did  take  place. 

Nannes  (49)  found  that  a  well  decomposed  peat  soil  contained 
0.166  percent  phosphorus.  He  found  that  0.057  percent  of  phos- 
phorus was  extracted  with  the  matiere  noire.  When  the  ammonia- 
cal  solution  of  the  matiere  noire  was  treated  with  hydrochloric  acid, 
0.039  percent  of  the  phosphorus  was  found  in  the  organic  precipi- 
tate. He  also  attempted  to  isolate  a  definite  organic  phosphorus 
compound  and  he  believed  that  he  detected  the  presence  of  lecithin 
and  chlorophyllan. 

Ladd  (43)  found  in  a  study  of  eight  samples  of  different  soil 
that  an  average  of  41  percent  of  the  phosphorus  was  associated 
with  the  extracted  matiere  noire;  the  variation,  however,  was 
from  10  percent  to  90  percent. 

In  a  later  article  (44)  he  showed  that  as  the  humus  of  the  soil 
increased  the  phosphorus  associated  with  the  extracted  matiere 
noire  also  increased.  From  the  fact  that  the  organic  precipitate, 
formed  by  neutralizing  the  ammoniacal  extract,  contained  the  phos- 
phorus he  concluded  that  it  existed  in  the  soil  in  organic  combina- 
tion, but  just  what  the  relationship  was  not  clear. 

Emmerling  (52)  believed  that  there  were  four  forms  of  phos- 
phorus in  the  soil,  one  of  which  was  phosphorus  in  organic  com- 
bination. 

Rimbach  (53)  found  6.15  percent  P2  65  in  the  ash  of  the 
matiere  noire  which  was  precipitated  from  the  ammoniacal  solu- 
tion by  the  addition  of  gypsum  and  magnesium  sulfate. 

Nagaoka  (57)  found  that  ignition  of  the  soil  for  fifteen  min- 
utes at  a  faint  red  heat  materially  increased  the  availability  of  the 
phosphorus.  He  attributed  this  action  to  the  destruction  of  the 
humophosphates. 


/p/o]  CARBON,  PHOSPHORUS  AND  NITROGEN  IN  SOILS  101 

Aso  (58)  confirmed,  in  a  general  way,  the  results  obtained  by 
Schmoeger.  He  also  found  0.049  percent  of  lecithin  in  the  soil. 
He  drew  the  following  conclusions : 

1.  Phosphorus  existed    in  the  soil    as  inorganic    and  organic 
compounds. 

2.  The  organic  phosphorus  material  was  principally  nuclein 
with  a  very  small  part  of  lecithin. 

3.  Ignition  rendered  the  phosphorus  in  organic  combination 
available. 

Hartwell  and  Kellogg  (60)  found  that  an  average  of  one-half 
of  the  phosphorus  was  associated  with  the  organic  matter  in  the 
soil  taken  from  four  plots  which  had  received  different  treatment. 

Dumont  (62)  studied  a  complete  manure,  the  composition  of 
which  was  as  follows:  solnble  matter  (in  dilute  alkali)  50.4  per- 
cent; insoluble  matter  49.6  percent;  total  nitrogen  1.6  percent; 
total  phosphorus  1.27  percent. 

The  soluble  portion  contained  35  percent  of  the  nitrogen  and 
46  percent  of  the  phosphorus.  In  order  to  obtain  data  upon  the 
state  of  combination  of  the  phosphorus,  the  ammoniacal  solution 
of  mailer e  noire  was  treated  with  various  reagents  with  the  result 
(recalculated  to  the  element  basis)  shown  in  Table  4. 

TA.BI,E  4.— DISTRIBUTION  OF  PHOSPHORUS  WHEN  MATIERE  NOIRE  is 
PRECIPITATED 


Precipitating  agent 

Phosphorus 

In  precipitate 

In  filtrate 

Citric  acid         ... 

0.383 
0.386 
0.532 
0.566 
0.5S4 

0203 
0.199 

0.053 
0.019 
0.0009 

Hydrochloric  acid  

Alumi  nium  sulf  ate  

Calcium  chlorid  

These  results  furnished  conclusive  proof  to  Dumont  that  a  part 
of  the  phosphorus  of  the  soil  was  in  organic  combination. 

Later  (64)  he  obtained  better  cultural  results  from  application 
of  humic  phosphatic  manures  than  from  mineral  phosphatic  ma- 
nures and  better  even  than  from  barnyard  manure,  which  he  at- 
tributed to  the  phosphorus  in  organic  combination. 

In  a  still  later  article  (65)  he  said  that  the  organic  phosphorus 
was  derived  from  two  sources :  first,  from  the  nuclein  and  lecithin 
of  the  decaying  vegetable  and  animal  debris ;  second  from  the 
union  of  the  humus  with  the  water  soluble  phosphates  of  the  soil. 

Evidence  of  the  latter  contention  was  obtained  by  precipitating 
the  matiere  noire  in  the  presence  of  potassium  hydrogen  phosphate 
by  different  reagents  as  indicated  in  Table  5. 


102 


BULLETIN  No.  145 


[April, 


TABLE  5. — AMOUNT  o^  PHOSPHORUS  IN  PRECIPITATED  HUMUS  AND  FILTRATE 


Precipitating- 
agent 

Series  A 
Phosphorus  in- 
troduced=.087 

Series  B 
Phosphorus  in- 
troduced =  .218 

Series  C 
Phosphorus  in- 
troduced =  .437 

Phos- 
phorus 
in 
humus 

Phos- 
phorus 
in 
filtrate 

Phos- 
phorus 
in 
humus 

Phos- 
phorus 
in 
filtrate 

Phos- 
phorus 
in 
humus 

Phos- 
phorus 
in 
filtrate 

Acetic  acid  

0.056 
0.054 
0.057 
0.057 

0.031 
0.033 
0.030 
0.030 

0.057 
0.055 
0.059 
0.061 

0.160 
0.163 
0.158 
0.156 

0.058 
0.054 
0.059 
0.062 

0.374 
0.381 
0.378 
0.372 

Citric  acid  

Hydrochloric  acid 
Sulfuric  acid  

Altho  the  amount  of  dipotassium  phosphate  added  to  the 
solution  had  increased,  the  amount  of  phosphorus  absorbed  by  the 
humus  was  practically  constant,  due  to  the  formation  of  definite 
"composes  phospho-humique." 

Konig  (67)  found  that  hydrogen  peroxid  oxidized  from  40 
percent  to  70  percent  of  the  humus  present  in  the  soil  and  that 
much  more  of  the  phosphorus  was  soluble  in  pure  and  carbonated 
water  after  oxidation  than  before,  due,  he  believed,  to  the  destruc- 
tion of  the  organic  phosphorus  compounds. 

Fraps  (69),  quite  recently,  made  a  study  of  the  phosphorus 
extracted  from  the  soil  by  4  percent  ammonia  in  the  usual  deter- 
mination of  humus.  He  confirmed  Pitsch's  results  regarding  the 
possibility  of  some  of  the  ammonia-soluble  phosphorus  being  of 
inorganic  origin.  He  separates  the  ammonia-soluble  phosphorus 
into  three  classes  as  follows: 

1.  The  phosphorus  associated  with  the  clay  held  in  suspension 
in  the  liquid. 

2.  The  phosphorus  precipitated  with  the  organic  matter  when 
the  solution  was  neutralized  with  an  acid. 

3.  The  phosphorus  which  remained  in  solution  after  the  pre- 
cipitation of  the  organic  matter. 

With  the  soils  under  consideration  he  found  that  1/9  of 
the  ammonia-soluble  phosphorus  was  in  the  first  class,  1/3  was  in 
the  second  class  and  5/9  was  in  the  third  class. 

The  phosphorus  found  in  the  first  class  was  assumed  to  be  as- 
sociated with  the  clay  particles  as  iron  and  aluminium  phosphates. 
He  concluded  that  the  phosphorus  precipitated  with  the  organic 
matter  from  the  ammonical  solution  by  the  addition  of  acids  was 
in  organic  combination.  The  phosphorus  remaining  in  the  mother 
liquor  was  assumed  to  be  derived  from  the  iron  and  aluminium 
phosphates  of  the  soil. 

Mooers  and  Hampton  (77)  recently  proposed  a  method  for 
obviating  the  error  introduced  in  the  humus  determinations  by  the 


CARBON,  PHOSPHORUS  AND  NITROGEN  IN  SOILS  103 

suspended  clay.  They  claimed  that  filtration  through  the  Cham- 
berlain-Pasteur filter,  as  suggested  by  Cameron,  introduced  a 
serious  error  inasmuch  as  the  filter  absorbed  some  organic  matter. 
They  proposed  an  evaporation  method :  by  evaporation  of  the 
ammoniacal  extract  to  dryness  re-dissolving  in  ammonia  and  filtra- 
tion, several  times,  a  perfectly  clear  solution  was  obtained.  Deter- 
mination of  the  humus  in  this  filtrate  gave  very  concordant  results. 
Hopkins  and  Pettit  (68)  found  that  in  certain  soils  the  mineral 
composition  had  a  tendency  to  be  constant  in  the  surface,  sub- 
surface, and  subsoil.  This  was  indicated  by  the  uniform  "potassium 
content  of  the  surface,  subsurface,  and  subsoil  and  by  the  fact  that 
different  samples  of  surface  soil  of  the  same  type  showed  a  wide 
variation  in  the  phosphorus  content  but  that  this  variation  largely 
disappeared  in  the  subsoil.  The  potassium  exists  in  the  soil  in  the 
inorganic  form,  the  nitrogen  exists  chiefly  jn  the  organic  form  while 
the  phosphorus  may  exist  in  the  inorganic  and  organic  state.  They 
suggested,  therefore,  a  method  for  calculating  the  phosphorus  in 
the  organic  state  in  the  surface  soil.  The  difference  in  amount  of 
nitrogen  in  the  surface  soil  'and  subsoil,  and  the  difference  in  the 
amount  of  phosphorus  in  the  surface  soil  and  subsoil  gave  appar- 
ently the  amount  of  nitrogen  and  phosphorus  associated  together 
in  organic  combination.  By  means  of  this  ratio  and  the  total 
amount  of  nitrogen  in  the  surface  soil  the  total  amount  of  organic 
phosphorus  present  in  the  surface  soil  could  be  calculated. 

4.   CARBON  AND  NITROGEN  CONTENT  OF  FUNDAMENTAL  ROCKS 

The  fundamental  rocks  out  of  which  soils  have  been  formed 
contain  an  appreciable  amount  of  carbon  and  nitrogen  which  is  in- 
digenous to  them. 

Dellese  (3)  discovered  that  mineral  matter,  crystalline,  sedi- 
mentary and  eruptive  contained  carbon  associated  with  nitrogen. 
This  mineral  matter,  which  was  formed  under  similar  conditions 
of  temperature,  pressure,  etc.,  had  a  tendency  to  contain  a  constant 
amount  of  carbon  and  nitrogen. 

The  work  of  Lawes  and  Gilbert  (16),  Dyer  (55)  and  Hall  and 
Miller  (66)  on  the  clays  and  other  fundamental  rock  material 
taken  from  various  great  depths  indicated  that  an  appreciable 
amount  of  carbon  and  nitrogen  was  indigenous  to  the  underlying 
soil  material. 


jp/o]  CARBON,  PHOSPHORUS  AND  NITROGEN  IN  SOILS  105 

(B)    EXPERIMENTAL  PART 

The  starting  point  of  such  an  investigation  consists  of  a  con- 
sideration from  a  mathematical  point  of  view  of  the  existing  data 
regarding  the  relationships  of  carbon,  phosphorus  and  nitrogen  of 
the  soil. 

i.    MATHEMATICAL 


(a)     INFlyUENClv  OF  AGE  UPON  THE   NITROGEN-CARBON   RATIO 

From  the  data  available  in  the  literature  it  is  possible  to  deter- 
mine within  certain  limits  the  influence  of  age  upon  the  nitrogen- 
carbon  ratio  in  soils.  From  the  average  results  of  a  number  of 
nitrogen  determinations  (68)  and  the  carbon  content  obtained  by 
calculation  from  the  proximate  analysis,  it  is  possible  to  determine 
the  approximate  nitrogen-carbon  ratio  in  the  more  common  humus 
producing  materials.  The  results  obtained  in  this  way  will  be 
found  in  Table  6.  The  materials  naturally  fall  into  two  groups  : 
in  the  first  group  the  ratio_  varies  from  i  152.2  for  corn  stover  to 
1  184.1  for  wheat  straw;  in  the  second  group  the  variation  is  from 
i  :i6.7  for  alfalfa  hay  to  i  135.4  for  timothy  hay. 

TABI«E  6.  —  APPROXIMATE  NITROGEN-CARBON  RATIO  IN  THE  MORE  COMMON 
HUMUS  PRODUCING  MATERIALS 


Kind  of  material 

Carbontol 
of  nitrog-en 

Corn  stover     ... 

52.2 

Oat  straw         .                           ... 

67  8 

84.1 

Timothy  hay  .... 

35  4 

Clover  hay  

21.3 

19.5 

Alfalfa  hay  

16.7 

3  2 

£ein  

3  4 

2.8 

In  Table  6  will  also  be  found  the  nitrogen-carbon  ratio  in  some 
of  the  compounds  which  might  be  expected  to  be  found  in  humus. 
The  ratio  is  very  narrow  and  does  not  vary  much  from  i  13. 

The  next  step  in  the  study  in  the  influence  of  age  upon  the 
nitrogen-carbon  ratio  would  be  to  determine  the  ratio  in  as  fresh 
humus  as  possible  from  known  materials.  Snyder  (35)  in  his 
study  of  the  production  of  humus  from  known  materials  placed  a 
weighed  quantity  of  the  material  together  with  a  weighed  quantity 


106 


BULLETIN  No.  145 


[April, 


of  soil  having  a  low  humus  content  in  a  box  and  set  aside  for  one 
year.  At  the  end  of  the  experiment  the  humus  was  extracted  and 
the  carbon  and  nitrogen  determined  in  the  inatiere  noire.  At  first 
thought  this  would  appear  to  furnish  the  desired  information,  but 
unfortunately  no  check  was  run  with  the  untreated  soil,  so  no  cor- 
rection can  be  made  for  the  carbon  and  nitrogen  which  may  have 
been  converted  into  humus  from  the  unhumified  material  of  the 
soil.  This  is  evidently  not  a  quantity  which  can  be  ignored  since 
the  humus  content  of  the  original  soil  is  .06  percent  while  the  total 
nitrogen  of  the  soil  is  .02  percent  showing  that  considerable  un- 
humified organic  matter  was  present,  otherwise  the  humic  nitrogen 
would  be  33.33  percent  while  it  has  been  shown  (71)  that  the 
humic  nitrogen  would  more  probably  be  nearer  5  percent.  In  ad- 
dition, the  fact  that  the  humus  obtained  from  sugar  contains  some 
nitrogen  is  evidence  that  some  of  the  unhumified  organic  matter  of 
the  soil  has  been  converted  into  humus,  since  sugar  does  not  con- 
tain nitrogen.  The  results,  however,  will  be  found  in  Table  7.  In 

TABI,E  7. — MINNESOTA  Soil,  STUDIES:  HUMUS   PRODUCTION   FROM   KNOWN 

MATERIALS 


Percent 

Ratio  of 

Material  used 

Humus 

Carbon 
in  humus 

Nitrogen 
in  humus 

carbon  to  1 
of  nitrogen 

0.06 

? 

? 

? 

0.58 

41.95 

6.16 

6.8 

Clover  

0  37 

54.22 

8.24 

6.6 

Ivleat  scraps            . 

0  31 

48  77 

10  96 

4  5 

0  46 

54.30 

2.50 

21.7 

Flour  

0.47 

51.02 

5.02 

10.2 

Saw  dust  

0.59 

49.28 

0.32 

153.8 

Sugar  

0.32 

57.84 

0.08 

741.0 

the  first  five  substances  the  variation  is  from  i  :2i.7  for  oat  straw 
to  i  :4-5  for  meat  scraps. 

The  large  number  of  carbon  and  nitrogen  determinations  made 
in  the  soils  of  Illinois  (68)  rendered  it  possible  to  determine  the 
nitrogen-carbon  ratio,  not  only  for  the  surface  soil,  but  also  for 
the  subsurface  and  subsoil.  The  average  of  19  determinations  for 
the  soil  type,  gray  silt  loam  on  tight  clay,  gave  the  ratios  1 110.4, 
i  :8.8,  and  1 17.6  for  the  surface,  subsurface,  and  subsoil  re- 
spectively. The  ordinary  brown  silt  loam  soils  as  an  average  of 
68  determinations  gave  a  nitrogen-carbon  ratio  of  1:12.1,  1:11.5 
and  i  :8-9  for  the  surface,  subsurface,  and  subsoil  respectively.  The 
black  clay  loam  soils  as  an  average  of  25  determinations  gave 
i  111.7,  i  :II.Q  and  i  :g  respectively  in  the  surface,  subsurface,  and 
subsoil.  The  peat  soil  as  the  average  result  of  5  determinations 
gave  i  :ii.8  and  i  :i2.9  for  the  surface  and  subsoil  respectively. 


CARBON,  PHOSPHORUS  AND  NITROGEN  IN  SOILS 


107 


TABL.E  8  — RATIOS  OF  CARBON  AND  NITROGEN  IN  ILLINOIS  SOILS 


Soil 
type 
No. 

Soil  types 

No.  of 

analysis  on 
which 
calculations 
are  based 

Carbon  to  1  of  nitrogen 

Surface 

Sub- 
surface 

Subsoil 

330 
426 
526 
626 
726 
1126 
1026 

Gray    silt    loam    on 
tight  clay         .... 

19 
11 
8 
6 
4 
30  . 
9 

10.4 
12.5 
13.2 
11.4 
11.9 
11.9 
12.0 

8.8 
11.7 
12.9 
10.5 
11.1 
11.5 
11.5 

7.6 
9.6 

8.7 
8.7 
8.8 
8.6 
9.3 

Brown  silt  loam  .... 

Brown  silt  loam   .  .  . 

Brown  silt  loam  . 

Brown  silt  loam  .... 

Brown  silt  loam  
Brown  silt  loam  

Averages 

68 

12.1 

11.5 

8.9 

420 
520 
1120 
1220 

Black  clay  loam  

v  7 
5 
11 

2 

12.2 
12.4 
11.1 
11.2 

12.2 
12.2 
11.1 
12.2 

8.9 
11.4 
8.3 
7.4 

Black  clay  loam  

Black  clay  loam  
Black  clay  loam.  .  .  . 

Averages 

25 

11.7 

11.9 

9.0 

1401 

5 

11.8 

12.9 

12.9 

The  Rothamsted  work  furnished  information  regarding  the 
nitrogen-carbon  ratio  of  the  soil  in  nine  inch  sections  to  a  depth  of 
90  inches.  These  results  will  be  found  in  Tables  9  and  10.  The 
ratio  for  the  Broadbalk  wheat  fields  varies  from  i  19.5  to  4.8  for 
the  surface  and  ninth  9  inches  respectively.  After  the  fifth  9  inches 
there  is  very  little  change  in  the  ratio.  In  the  Hoosfield  barley 
soils  the  ratio  varies  from  i  :io.6  to  i  :8.8  for  the  surface  and  sub- 
soil respectively. 

TABI,E  9.— BROADBALK  WHEAT  Soii,s:    RATIO  OF  CARBON  To  NITROGEN 


Perc 

.ent 

Depth 

Carbon 

Total   ni- 
trogen 

Carbon  to  1 
of  nitrogen 

jrjrst  c)  inches  (all  plats)           

1  155 

1222 

ox 

640 

0784 

Q  2 

Third  9  inches     

492 

0666 

7  4 

339 

0511 

6  6 

279 

0472 

5  9 

.256 

.0430 

5  9 

.248 

0420 

5  9 

215 

0396 

5  4 

Ninth  9  inches   

.189 

.0391 

4  8 

Tenth  9  inches  

.188 

.0375 

5.0 

TABI.E  10.— HOOSFIEI,D  BARLEY  Soii<s:    RATIO  OF  CARBON  To  NITROGEN 


Depth 

Carbon  to  1 
of  nitrogen 

10.6 

Second  9  inches   

8.8 

Third  9  inches       

8.8 

108 


BULLETIN  No.  145 


[April, 


Hall  and  Miller  (66)  reported  the  carbon  and  nitrogen  con- 
tent, and  ratio  of  carbon  to  nitrogen  in  samples  of  various  ma- 
terials taken  from  such  great  depths  as  to  preclude  all  possibility 
of  weathering.  Since  the  nitrogen  was  always  found  to  be  associ- 
ated with  carbon  it  was  regarded  as  being  of  organic  origin  and 
as  being'  derived  in  part  from  the  organic  matter  present  in  the 
clay  at  the  time  of  its  deposit.  These  results  are  shown  in  Table  n. 

TABI<B  11. — CARBON  AND  NITROGEN  IN  UNWEATHKRED  ROCKS 


No.  of 
soil 

Formation 

Depth  at 
whichsa  tu- 
ple was  ta- 
ken, ft. 

Percent 

C/  M 
Ratio 

Organic 
car  bo  n 

Nitrogen 

1 

2 
3 
4 
5 
6 
7 
8 
9 
10 
11 
12 
13 
14 

L/ower  Bagshot  Sand,  Weybrldge.  . 
Upper  Greensand,  Farnham,  Surrey 
Folkestone  Beds,  Brabourne,  Kent. 
L/ower  Greensand,  Sevenoaks  

18—20 
30 

20 
30 
130 
18 
30 
1236 
280—400 
920 
246 
570 
700 
10 

0.02 
0.032 
0019 
0.076 
0391 
0427 
0135 
1.938 
0.172 
0.548 
2.139 
0.387 
1.120 
0577 

.00384 
.00718 
.00453 
.00881 
.041 
.0415 
.0647 
.137 
.0325 
.0528 
.107 
.0455 
.0803 
.0294 

5.4 
4.5 
4.2 
8.7 
9.5 
10.3 
2.1 
14.1 
5.3 
10.4 
20.0 
8.5 
13.9 
19.6 

Gault  Clay,  Nackholt,  Kent  
Weald  Clay   Pluckley    Kent   

Carboniferous  Shale,  Barnsley  ... 
L/ower  Gault,  Dover  

Oxford  Clay  Dover       

Kimmeridge  Clay,  Welton  L/incs.  .  . 
Kimtneridge  Clay    Dover  

lyower  Lias,  Micketon,  Glos  

Clay  with  Flints,  Harpenden   

NOTES 

1.  A  grey  coarse  sand. 

2.  Pale  grey  fine  sandy  rock. 

3.  Coarse  yellowish  sand. 

4.  Fine  yellowish  sand. 

5.  Solid  grey  clay. 

6.  Solid  dark  green  clay. 

7.  Close  grey  and  red  mottled  clay. 

8.  Hard  grey  shale. 

9.  10,     12.     Hard  grey  clays  from  the  coal  pit  shafts  at  Dover. 
11.  Hard  grey  clay. 

13.  Hard  grey  clay. 

14.  Reddish  sandy  brick  earth. 

It  will  be  seen  from  a  study  of  the  above  tables  that  under 
normal  conditions  the  nitrogen-carbon  ratio  of  the  soil  has  a  tend- 
ency to  become  narrower  as  the  age  of  the  organic  material  in- 
creases. The  ratio,  however,  never  becomes  narrower  or  ever 
equal  to  the  ratio  of  the  more  common  proteins  contained  in  the 
humus  producing  materials. 

(b)      CARBON,    NITROGEN    AND    PHOSPHROUS   IN    ILLINOIS    SOILS 

Before  discussing  the  phosphorus-carbon  and  phosphorus- 
nitrogen  ratios  in  the  soil  it  seemed  desirable  to  determine  as  closely 
as  possible  these  ratios  in  fresh  material  out  of  which  humus  might 
be  formed. 


jp/o] 


CARBON,  PHOSPHORUS  AND  NITROGEN  IN  SOILS 


109 


TABLE  12.— APPROXIMATE  CARBON-PHOSPHORUS  AND  NITROGEN-PHOSPHORUS 
RATIOS  IN  THE  MORE  COMMON  HUMUS  PRODUCING  MATERIALS 


Kind  of  material 

Carbon  to  1 
of  phospho- 
rus. 

Nitrogen  to 
1  of  phos- 
phorus 

Corn  stover  
Oat  straw 

417 

420 

8.0 
6.2 

Wheat  straw  

525 

6.2 

Timothy  hay           

283 

8.0 

Clover  hay  

171 

8.0 

Cowpea  hay       .               ... 

181 

9.3 

Alfalfa  hay  

186 

11.1 

Nuclein  

3.7 

1.4 

The  ratios  in  the  more*  common  humus  producing4  materials 
calculated  from  the  average  of  a  number  of  analysis  for  nitrogen 
and  phosphorus  (68),  will  be  found  in  Table  12."  In  the  coarser 
material  the  phosphorus-carbon  ratio  varies  from  i  1417  to  1 1525  : 
the  phosphorus-nitrogen  ratio  is  more  constant  being  i  :6.2  and  l  :8. 
In  the  hays,  the  phosphorus-carbon  ratio  varies  from  i  :i86  to  1 1283 
while  again  the  phosphorus-nitrogen  ratio  is  more  constant,  the 
variation  being  i  :ii.i  to  i  :8.  In  nuclein  the  ratios  are  I  13.7  and 
i  11.4  respectively. 

In  Table  13  will  be  found  the  phosphorus-carbon  and  phos- 
phorus-nitrogen ratios  obtained  by  calculation  from  the  Minnesota 
Soil  Studies.  The  phosphorus  determinations  which  were  reported 
as  phosphoric  anhydrid  were  first  recalculated  to  the  element  basis. 
Both  ratios,  it  will  be  observed,  are  very  narrow. 

In  Table  14  will  be  found  the  phosphorus-carbon  and  phos- 
phorus-nitrogen ratios  in  Illinois  soils  calculated  from  the  data  re- 
ported by  Hopkins  and  Pettit  (68).  The  average  of  7  calculations 
of  the  gray  silt  loam  on  tight  clay  gave  the  phosphorus-carbon  and 
phosphorus-nitrogen  ratios  as  i  142.6  and  i  113.8  respectively. 

TABLE  13.  —MINNESOTA  SOIL  STUDIES:    CARBON-PHOSPHORUS  AND  NITROGEN 

PHOSPHORUS  RATIOS 


Kind  of  material 

Carbon  to  1 
of  phospho- 
rus. 

Nitrogen  to 
1  of  phos- 
phorus 

Original  soil   

? 

? 

9.8 

1  4 

Clover                  

11  2 

1  7 

Ivleat  scraps     

9  7 

2  2 

38.2 

1.8 

Flour  

22  0 

2.2 

Saw  dust                 

37  0 

0  24 

42.4 

0.06 

• 
110 


BULLETIN  No.  145 


[April, 


TABI,E  14. — II,:LINOIS  SOILS:    ORGANIC  PHOSPHORUS;  RATIOS  OF  CARBON  TO 

PHOSPHORUS,  NITROGEN  TO  PHOSPHORUS  AND  CARBON  TO  NITROGEN, 

FACTORS  FOR  CALCULATING  THE  ORGANIC  PHOSPHORUS. 


Soil 
type 
No. 

Number  of  an- 
alysis on  which 
calculations 
are  based 

Organic  phos- 
phorus as  per- 
cent    of    total 
phosphorus 

Ratios  of 

Factors  for 
calculating  the 
organic    phos- 
phorus from 
the  organic 
carbon 

Carbon  to  1 
of  organic 
phosphorus 

Nitrogen  to 
1  of  organic 
phosphorus 

330                7 

24.4 

142. 

13.8 

0.007012 

426 
526 
626 
726 
1126 
1026 

9 
8 
5 
4 
24 
9 

34.4 
29.5 
13.9 
38.1 
40.9 
44.9 

132. 
185. 
298. 
133. 
116. 
125. 

10.6 
14.0 
25.1 
10.5 
9.9 
10.9 

0.007570 
0.005393 
0.003348 
0.007491 
0.008583 
0.007988 

Average       59 

33.5 

165. 

13.5 

0.006053 

420 
520 
1120 
1220 

7 
5 
11 

2 

36.0 
33.8 
46.2 
32.4 

134. 
260. 
90. 
169. 

10.3 
12.0 

8.3 
15.2 

0.007441 
0.003836 
0.005907 
0.002956 

Average        25 

37.1 

163. 

11.4 

0.006113 

1401 
1401 

4 
(b)       5 

100.0 
100.0 

230. 
338. 

19.6 
26.5 

0.004311 
0.002956 

(b)    Subsoil  (7"— 40") 

The  ordinary  brown  silt  loam  soils,  as  an  average  of  59  deter- 
minations, gave  the  ratios  of  1 1165.2  and  i  :i3-5  respectively.  The 
black  clay  loam  soils,  as  an  average  of  25  calculations,  gave  the 
ratios  of  1 1163  and  i  :ii-4  respectively.  The  ratios  in  the  surface 
peaty  soil,  assuming  all  the  phosphorus  to  be  in  the  organic  state, 
are  1 1230  and  1 119.6.  The  ratios  in  the  subsoil  of  the  peaty  soil 
are  somewhat  wider,  being  i  1338  and  1 126.5  respectively. 

(c)     FACTORS   FOR   CALCULATING  ORGANIC   PHOSPHORUS 

By  means  of  the  carbon-phosphorus  ratios  established  as  in- 
dicated above,  it  is  possible  to  develop  factors  for  calculating  the 
amount  of  the  organic  phosphorus  in  the  surface  soil  from  the 
total  organic  carbon.  For  example  the  carbon-phosphorus  ratio, 
1 1163,  in  the  black  clay  loam  soils  means  that  for  every  part  of 
organic  phosphorus  there  are  163  parts  of  carbon  or  for  each  part 
of  organic  carbon  there  are  0.006113  Pai*ts  of  organic  phosphorus. 
Hence  by  multiplying  the  amount  of  organic  carbon  by  the  latter 
number  the  amount  of  organic  phosphorus  may  be  obtained. 

The  factors  as  developed  will  be  found  in  the  last  column  of 
Table  14.  It  is  hoped  that  they  will  be  of  value  in  drawing  broad 
general  conclusions  regarding  organic  phosphorus  of  the  soil  from 
a  number  of  analyses.  The  variations  in  the  various  samples  con- 
sidered in  any  single  type  are  too  great  to  permit  the  utilization  of 
the  factors  in  isolated  cases. 


jp/o] 


CARBON,  PHOSPHORUS  AND  NITROGEN  IN  SOILS 


111 


It  will  be  observed  that  from  1/4  to  2/5  of  the  total  phos- 
phorus of  the  several  soil  types  considered  is  in  organic  combina- 
tion. These  results  indicate  that  a  larger  amount  of  phosphorus 
is  in  organic  combination  than  the  work  of  some  American  inves- 
tigators would  lead  us  to  believe. 

2.    CHEMICAL 


(a)     ANALYTICAL,  RKSUL/TS  OF  SOIL  FROM   ILLINOIS   SOUTH 

FARM 


A  sample  of  soil  for  a  study  of  the  organic  phosphorus,  by  the 
available  methods  for  the  determination  of  the  organic  phosphorus 
of  the  soil,  was  obtained  from  the  Illinois  South  Experimental 
Farm.  This  soil  is  the  ordinary  brown  silt  loam  soil  of  the  corn 
belt. 

The  total  potassium,  carbon,  nitrogen,  and  phosphorus  in  the 
surface  and  subsoil  were  determined  by  the  methods  adopted  by 
the  Illinois  Experiment  Station.  The  results,  expressed  as  pounds 
per  two  million  pounds  of  dry  soil,  will  be  found  in  Table  15.  The 
average  potassium  content  of  36,700  pounds,  and  37,070  pounds  in 
the  surface  and  subsoil  indicate  a  constant  mineral  composition, 
hence  the  calculation  method  may  be  safely  applied  for  the  deter- 
mination of  the  organic  phosphorus.  The  amount  of  organic  phos- 
phorus, the  various  ratios  and  the  developed  factor  will  be  found 
in  Table  16.  It  will  be  seen  that  46  percent  of  the  total  phosphorus 
in  this  soil  is  in  organic  combination. 


TABLJE;  IS. — ANAI,YTICAI,  RESUI/TS  OF  Soil,  FROM  ILLINOIS  SOUTH  KXPF.RI- 
MENTAI,  FARM:  RESULTS  EXPRESSED  AS  POUNDS  IN  Two  MILLION 
POUNDS  OF  DRY  Soil, 


Soil  No. 

Soil 
stratum 

Potassium 

Carbon 

Nitrogen 

Phos- 
phorus* 

1A 
IB 

Surface 
Surface 

36280 
37120 

41800 
42180 

3760 
3844 

938 
901 

Average 

Surface 

36700 

41^90 

3802 

919* 

3A 
3B 

Subsoil 
Subsoil 

36600 
37540 



1735 
1680 

702 
670 

Average 

Subsoil 

37070 

1708 

686 

*L/ater  inspection  of  the  strip  of  land  from  which  this  sample  was  taken  led  to  the  conclu 
sion  that  it  may  have  been  modified  by  a  previous  disturbance  of  the  soil  in  putting-  in  tile 
drainage;  and  a  composite  sample  was  subsequently  collected  at  points  a  short  distance  from 
the  tile  drain  which  showed  985  pounds  of  phosphorus  instead  of  919  pounds.  The  possible 
influence  of  this  difference  should  be  kept  in  mind.  Thus  the  percent  of  total  phosphorus  in 
org-anic  form  would  be  reduced  from  46  percent  to  43  percent.— C.  G.  Hopkins. 


112 


BULLETIN  No.  145 


[April, 


TABLE  16 — ORGANIC  PHOSPHORUS:  RATIOS  OF  CARBON  TO  ORGANIC  PHOS- 
PHORUS, NITROGEN  TO  1  ORGANIC  PHOSPHORUS,  CARBON  To  NITROGEN 
IN  SURFACE  Son, 


Pounds  of 
organic 
phosphorus 
in  two 
million 
pounds  of 
soil 

Org-anic 
phosphorus 
as  percent 
of  total 
phosphorus 

Ratios  of 

Factor  for 
calculating- 
the  organic 
phosphorus 
from  organic 
carbon 

Nitrogen 
to  1  org-anic 
phosphorus 

Carbon  to 
1  nitrogen 

Carbon  to 
1  organic 
phosphorus 

423 

46.0 

9.0 

11.1 

99.2 

0.01008 

(b)     PHOSPHORUS  ASSOCIATED  WITH  THE  MATIERE  NOIRE 

Of  the  two  available  methods  for  determining1  the  organic 
phosphorus,  the  one,  the  determination  of  the  phosphorus  associ- 
ated with  the  matier e  noire  extracted  from  the  soil  by  4  percent 
ammonia,  has  given  rise  to  some  confusion.  Grandeau  (10)  re- 
garded the  phosphorus  extracted  with  the  matiere  noire  as  being 
probably  in  organic  combination.  Eggertz  (21),  Nilson  (79), 
Wiklund  (25),  Dumont  (65),  Ladd  (43)  and  Snyder  (41)  also 
regarded  it  as  organic  in  form.  Pitsch  (14)  and  Van  Bemmelen 
(23)  took  the  opposite  view.  Pitsch  thought  that  part  of  the  ex- 
tracted phosphorus  may  have  been  derived  from  the  inorganic 
phosphates  of  the  soil.  Van  Bemmelen  regarded  the  phosphorus 
precipitated  with  the  matiere  noire  as  absorbed  phosphorus.  Quite 
recently,  Fraps  (69)  concluded  that  only  1/3  of  the  phosphorus  ex- 
tracted by  ammonia  was  in  organic  combination,  while  still  later 
Stoddart  (80)  concluded  that  only  1/5  of  the  extracted  phosphorus 
was  in  organic  combination.  As  a  result  of  this  conflicting  evi- 
dence there  is  considerable  confusion  regarding1  the  nature  of  the 
phosphorus  extracted  by  ammonia.  One  cause  of  this  confusion, 
no  doubt,  is  the  difficulty  of  getting  rid  of  the  suspended  clay, — 
ordinary  filtration  will  not  remove  it.  Obviously  all  of  the  phos- 
phorus associated  with  the  suspended  clay  should  not  be  included 
with  the  organic  phosphorus,  altho  part  of  it  may  be  organic  in 
form.  Fraps  removed  the  clay  by  precipitation  with  ammonium 
sulfate.  There  is  no  evidence,  however,  that  this  reagent  does 
not  also  precipitate  some  organic  matter  either  chemically  or  me- 
chanically. Ammonium  sulfate  is  used  by  physiological  chemists 
to  precipitate  the  proteins  in  order  to  make  certain  group  separa- 
tions, while  some  preliminary  work  here  showed  that  complete 
saturation  of  the  ammoniacal  extract  of  the  soil  with  ammonium 
sulfate,  after  the  removal  of  the  suspended  clay,  produced  a  heavier 
qualitative  precipitate  of  organic  matter  than  did  the  addition  of 
hydrochloric  acid.  It  would  seem,  therefore,  that  the  evaporation 
method  of  Hampton  and  Mooers  (77)  is  more  desirable  for  the 


CARBON,  PHOSPHORUS  AND  NITROGEN  IN  SOILS  113 

removal  of  the  suspended  clay.  Unless  otherwise  stated  the  latter 
method  was  used  for  the  removal  of  the  suspended  clay  in  all  the 
work  reported  in  this  paper. 

Owing-  to  the  conflicting  evidence  regarding  the  phosphorus  as- 
sociated with  the  extracted  matiere  noire,  it  seemed  desirable  to  do 
some  work  with  this  material  other  than  the  simple  determination 
of  the  phosphorus. 

The  soil,  without  previous  treatment  with  hydrochloric  acid  to 
remove  the  calcium,  was  extracted  with  4  percent  ammonia  in  the 
ratio  of  i  part  of  soil  to  50  parts  of  ammonia  water  for  36  hours 
as  in  the  usual  humus  determinations.  The  clay  was  removed  by 
evaporation  and  the  matiere  noire  was  obtained  in  quantity  for 
study.  Conditions  here  are  such  that  the  maximum  quantity  of  in- 
organic phosphorus  should  *be  found  in  the  ammoniacal  extract 
since  none  has  previously  been  removed  by  treatment  with  a  min- 
eral acid  as  in  the  usual  humus  determinations. 

The  suspended  clay  removed  by  evaporation  was  analyzed  for 
carbon  and  phosphorus  with  results  as  follows :  Carbon  3.73  per- 
cent and  3.61  percent,  or  an  average  of  3.67  per  cent;  phosphorus 
0.118  percent  and  0.109  percent,  or  an  average  of  0.113  percent. 
Since  the  carbon  in  the  original  soil  was  only  2.09  percent  while 
the  phosphorus  was  .046  percent,  the  relative  increase  of  carbon 
and  phosphorus  in  the  suspended  clay  indicates  undoubtedly  the 
accumulation  of  organic  matter  with  the  "clay."  It  would  appear 
probable  that  the  grinding  of  the  sample  of  soil,  while  preparing 
it  for  analysis,  would  convert  the  organic  matter  into  an  im- 
palpable powder  which  would  have  a  tendency  to  remain  sus- 
pended in  the  liquid  tog-ether  with  the  fine  clay  particles  when  the 
soil  was  extracted  with  ammonia, 

The  amount  of  the  extracted  matiere  noire  was  determined. 
It  was  then  analyzed  for  carbon,  nitrogen,  and  phosphorus.  The 
carbon  was  determined  by  the  method  suggested  by  Pettit  and 
Schaub  (59).  The  total  nitrogen  was  determined  by  the  regular 
Kjeldahl  method ;  correction  was  then  made  for  the  absorbed  am- 
moniacal nitrogen  by  determining  the  latter  in  a  separate  sample 
by  distillation  with  magnesium  oxide.  The  phosphorus  was  de- 
termined by  igniting  a  sample  of  the  matiere  noire  and  treating 
the  ash  with  aqua  regia;  the  silica  was  removed  by  evaporation 
and  the  phosphorus  determined  by  the  usual  volumetric  method.  A 
confirmatory  test  made  by  determining  phosphorus  by  fusion  with 
sodium  peroxid  gave  0.835  percent  and  0.815  percent  phosphorus 
in  the  matiere  noire  while  the  method  adopted  gave  0.860  percent 
and  0.830  percent. 

The  results  obtained  expressed  as  pounds  per  two  million 
pounds  of  soil  are  recorded  in  Table  17. 


114 


BULLETIN  No.  145 


[April. 


17. — Matter e  Noire,  CARBON,    NITROGEN  AND   PHOSPHORUS  IN  THE 
MATIERE  NOIRE;  RESULTS  EXPRESSED  AS  POUNDS  PER  TWO 

MILLION  POUNDS  OF  DRY  SOIL. 
(Soil  not  acid-extracted  before  treatment  with  ammonia) 


Number 

Matiere  Noire 

Carbon   in  the 
Matter  e  Noire 

Nitrogen  in 
the 
Mature  Noire 

Phosphorus 
in  the 
Matter  e  Noire 

A 
B 

27600 
28600 

10870 
10850 

1642 
1662 

233 
242 

Average 

28100 

10860 

1652 

238 

Phosphorus-nitrogen  ratio  ==  i  '.6.9 
Nitrogen-carbon  ratio  =  i  :6.6 
Phosphorus-carbon  ratio  —  1 145.6. 

The  matier  e  noire  was  now  redissolved  in  dilute  ammonia,  an 
excess  of  i  percent  hydrochloric  acid  added  and  set  aside  over 
night.  The  precipitate  of  organic  matter  was  brought  on  to  a  filter 
paper,  which  had  previously  been  dried  at  uo°C  and  weighed. 
The  precipitate  was  washed  with  i  percent  hydrochloric  acid,  dried 
at  no°C  and  weighed.  The  precipitated  matter  e  noire  was  obtained 
in  quantity  and  analyzed  for  carbon,  nitrogen  and  phosphorus.  The 
results  obtained  are  recorded  in  Table  18. 

TABLE  18. — PERCIPITATED  Matibre  Noire,  CARBON,  NITROGEN  AND  PHOS- 
PHORUS IN  PRECIPITATED  Mature  Noire:  RESULTS  EXPRESSED  AS 
POUNDS  PER  Two  MILLION  POUNDS  OF  DRY  SOIL 

(Soil  not  acid-extracted  before  treatment  with  ammonia) 


Number 

percipitated 
Mati&re  Noire 

Carbon  in 
precipated 
Matiere  Noire 

Nitrogen  in 
precipitated 

Matiere  Noire 

Phosphorus  in 
precipitated 
Matibre,  Noire 

A 
B 

9174 
9203 

4262 
4303 

604 
628 

20 
18 

Average 

9189 

4282 

616 

19 

Phosphorus-nitrogen  ratio  =  1 132.4 
Nitrogen-carbon  ratio  =  1 17 
Phosphorus-carbon  ratio  ==  1 1225 

The  results  recorded  in  Tables  17  and  18  are  very  significant 
as  can  be  more  readily  seen  by  glancing  at  Table  19  which  sum- 
marizes the  above  data. 

TABLE  19. — Matiere  Noire,  CARBON,  NITROGEN  AND  PHOSPHORUS  PRECIPI- 
TATED FROM  AMMONIACAL  SOLUTION  BY  HYDROCHLORIC  ACID:  RESULTS 
EXPRESSED  AS  PERCENT  OF  TOTAL  SOLUBLE  IN  AMMONIA. 
(Soil  not  acid-extracted  before  treatment  with  ammonia) 


Matibre  Noire 

Carbon 

Nitrogen 

Phosphorus 

32.7 

39.4 

37.3 

8.0 

CARBON,  PHOSPHORUS  AND  NITROGEN  IN  SOILS 


115 


Of  the  total  matter e  noire  obtained,  only  32.7  percent  has  been 
precipitated  from  the  alkaline  solution  by  hydrochloric  acid.  The 
portion  remaining  in  solution  does  not  consist  of  inorganic  salts, 
as  might  be  supposed,  as  is  readily  shown  by  the  fact  that  only 
39.4  percent  of  the  carbon  and  37.3  percent  of  the  nitrogen  has 
been  precipitated.  This  shows  conclusively  that  only  about  1/3  of 
the  dissolved  organic  matter  has  been  precipitated. 

Only  8.0  percent  of  the  total  soluble  phosphorus,  or  19  pounds 
out  of  238  pounds,  has  been  precipitated  from  alkaline  solution  by 
hydrochloric  acid.  Has  the  phosphorus  remaining  in  solution  in 
the  mother  liquor  been  derived  from  organic  or  inorganic  sources? 
The  fact  that  60.6  percent  of  the  carbon  and  62.7  percent  of  the 
nitrogen  also  remain  dissolved  in  the  mother  liquor  would  appear 
to  be  significant. 

Having  made  a  study  of  the  matiere  noire  obtained  from  the 
original  soil  it  seemed  desirable  to  investigate  the  matiere  noire 
obtained  in  the  usual  way  after  the  soil  had  been  extracted  with 
i  percent  hydrochloric  acid  to  remove  the  calcium  and  magnesium. 
It  seemed  reasonable  to  suppose  that  the  acid  extraction  would  re- 
move also  a  considerable  quantity,  if  not  all,  of  the  inorganic  phos- 
phorus, which  may  have  previously  passed  into  the  ammonia  so- 
lution. 

As  before,  the  amount  of  matiere  noire  was  determined  and 
then  extracted  in  quantity  for  the  determination  of  carbon,  nitrogen 
and  phosphorus.  The  results  obtained  will  be  found  in  Table  20. 

TABLE  20. — Mati&re  Noire,  CARBON,  NITROGEN  AND  PHOSPHORUS  IN  THE 
Matiere  Noire:     RESUI/TS  EXPRESSED  AS  POUNDS  PER  Two 

MILLION  POUNDS  OF  DRY  Soil, 
(Soil  acid  extracted  before  treatment  with  ammonia) 


Number 

Matiere  Noire 

Carbon  in  the 
Mati&re  Noire 

Nitrogen  in 
the 
Matiere  Noire 

Phosphorus 
in  the 

Matiere  Noire 

A 
B 

60840 
61660 

25860 
25790 

2805 
2885 

524 
508 

Average 

61250 

25825 

2845 

516 

Phosphorus-nitrogen  ratio  —  I  15.5 
Nitrogen-carbon  ratio  =  1 19.1 
Phosphorus-carbon  ratio  =  1 150 

The  matiere  noire  was  redissolved  in  dilute  ammonia  and  an 
excess  of  i  percent  hydrochloric  acid  added.  The  amount  of  the 
precipitate  and  the  carbon,  nitrogen  and  phosphorus  in  the  precipi- 
tate were  determined  as  before.  The  results  obtained  are  recorded 
in  Table  21. 


116 


BULLETIN  No.  145 


[April, 


TABLE  21. ^-PRECIPITATED  Matiere  Noire;  CARBON,  NITROGEN  AND  PHOSPHO- 
RUS IN  THE  PRECIPITATED  Matiere  Noire:    RESULTS  EXPRESSED  AS 

POUNDS  IN  Two  MILLION  POUNDS  OK  DRY  SOIL 
(Soil  first  acid-extracted  before  treatment  with  ammonia) 


Number 

Precipitated 
Mati&re  Noire 

Carbon  in 
precipitated 
Matter  c  Noire 

Nitrog-en  in 
precipitated 
Matiete   Noire 

Phosphorus  in 
precipitated 
Matiere  Noire 

A 
B 

30110 
31140 

11410 
11555 

1242 
1198 

57 
56 

Average 

30625 

11482 

1220 

56 

Phosphorus-nitrogen  ratio  ==  i  121.7 
Nitrogen-carbon  ratio  —  i  19.5 
Phosphorus-carbon  ratio  —  1 1205 

Table  22  summarizes  the  results  reported  in  Tables  20  and  21. 
Of  the  total  dissolved  matiere  noire  only  50  percent  was  precipi- 
tated. Again  the  greater  part  of  the  carbon  and  nitrogen  remain 
in  the  mother  liquor.  Only  44.5  percent  of  the  carbon  and  42.9 
percent  of  the  nitrogen  were  precipitated  while  but  8.7  percent  of 
the  phosphorus  was  precipitated. 

TABLE  22. — Matiere  Noire;  CARBON,  NITROGEN  AND  PHOSPHORUS  PRECIPI- 
TATED FROM  AMMONIACAL  SOLUTION  BY  HYDROCHLORIC  ACID:  RESULTS 
EXPRESSED  AS  PERCENT  OF  TOTAL  SOLUBLE  IN  AMMONIA 
(Soil  first  acid-extracted  before  treatment  with  ammonia) 


Matiere  Noire 

Carbon 

Nitrogen 

Phosphorus 
877 

50.0 

44.5 

42.9 

Again,  the  question  regarding  the  source  of  the  phosphorus 
remaining  in  solution  arises.  It  will  be  seen  that  55.6  percent  of 
the  soluble  carbon  and  58.1  percent  of  the  soluble  nitrogen  also  re- 
main in  solution.  Attention  should  be  called  to  the  fact  that  when 
the  original  soil  was  treated  direct  with  ammonia,  without  previ- 
ous extraction  with  hydrochloric  acid,  under  conditions  where  the 
maximum  amount  of  inorganic  phosphorus  should  be  dissolved, 
only  238  pounds  of  phosphorus  per  two  million  pounds  of  soil 
were  obtained :  yet,  after  the  soil  had  been  treated  with  hydro- 
chloric acid  to  remove  the  calcium,  under  conditions  where  the 
minimum  amount  of  inorganic  phosphorus  would  be  dissolved  by 
ammonia,  516  pounds  of  phosphorus  per  two  million  pounds  of 
soil  were  obtained.  The  difference  between  these  two  numbers, 
278  pounds,  unquestionably  represents  phosphorus  which  must  have 
been  derived  from  organic  sources.  Now,  since  only  55  pounds  of 
phosphorus  is  precipitated  with  the  matiere  noire  by  hydrochloric 
acid,  it  would  appear  that  the  organic  phosphorus  associated  with 
the  precipitated  mattere  noire  is  only  a  very  small  part  of  the  or- 
ganic phosphorus  present  in  the  soil. 


1910} 


CARBON,  PHOSPHORUS  AND  NITROGEN  IN  SOILS 


117 


Schmoeger  (39)  has  demonstrated  that  the  organic  phos- 
phorus compounds  of  the  soil  are  decomposed  by  heating  under 
pressure.  It  would  appear  probable,  therefore,  that  the  simple 
evaporation  of  the  ammoniacal  solution  on  the  water  bath  in  the 
preparation  of  the  mailer  e  noire  in  quantity  for  analysis  would 
cause  a  decomposition  of  the  phosphorus  compounds;  hence  when 
the  matiere  noire  is  redissolved  and  precipitated  by  hydrochloric 
acid,  less  phosphorus  would  be  obtained  in  the  precipitate  than 
would  be  the  case  if  the  material  had  not  been  heated.  This  idea 
was  confirmed  by  experimental  evidence  as  is  shown  in  Table  23. 
The  precipitated  matiere  noire  obtained  from  the  original  soil, 
which  had  not  been  extracted  with  hydrochloric  acid,  showed  19 
pounds  of  phosphorus  per  two  million  pounds  of  soil.  A  portion 
of  the  ammoniacal  extract  o"f  this  soil  was  freed  from  clay  by 
Frap's  method;  an  aliquot  part  of  the  extract  was  then  neutralized 
with  hydrochloric  acid  :  the  precipitate  obtained  showed  68  pounds 
of  phosphorus  per  two  million  pounds  of  soil,  or  over  three  times 
as  much  as  did  the  precipitate  obtained  from  the  evaporated  ma- 
terial. 


23.  —  PHOSPHORUS  IN  PRECIPITATED  Matikre  Noire:    RESULTS  E}x- 
PRESSED  AS  POUNDS  PER  Two  MILLION  POUNDS  OF  DRY  Son, 


Soil  not  acid-extracted 

Soil  acid-extracted 

Number 

Phosphorus 
in  heated 
Matibre  Noire 

Phosphorus 
in  unheated 

MatibreNoire 

Phosphorus 
in  heated 

Mati&re  Noire 

Phosphorus 
in  unheated 
MatiereNoire 

Phosphorus 
in  barium 
precipitate 

A 
B 

20 
18 

61 

77 

56 

57 

133 
164 

133 
138 

Average 

19 

69 

56 

149 

135 

The  acid  extracted  soil  gave  similar  results :  the  precipitated 
matiere  noire  which  had  been  subjected  to  heat  gave  only  55 
pounds  of  phosphorus  per  two  million  pounds  of  soil,  while  the 
precipitated  matiere  noire  which  had  not  been  subjected  to  heat 
gave  149  pounds  or  nearly  three  times  as  much.  The  latter  result 
was  again  confirmed.  When  the  ammoniacal  extract,  freed  from 
clay  by  precipitation  with  ammonium  sulfate,  is  treated  with 
barium  chloride,  the  organic  matter  is  quantitatively  precipitated 
as  is  indicated  by  the  decolorizing  of  the  supernatent  liquid  and  by 
the  fact  that  evaporation  of  the  filtrate  and  ignition  of  the  residue 
^gives  only  a  very  faint  charring.  But  unfortunately  the  barium 
Vhloride  also  precipitates  the  inorganic  phosphorus  as  barium 
phosphate  under  these  conditions,  and  when  the  liquid  is  rendered 
acid  it  becomes  colored,  showing  that  organic  matter  as  well  as 
inorganic  phosphorus  has  been  dissolved.  However,  the  precipi- 
tate was  separated  by  filtration,  washed  with  hydrochloric  acid  un- 


118  BULLETIN  No.  145  [April, 

til  free  from  barium  and  the  phosphorus  determined.  This  phos- 
phorus must  have  been  derived  from  organic  sources.  The  results 
are  recorded  in  the  last  column  of  Table  23  and  compare  very  well 
with  those  previously  obtained. 

According  to  Schmoeger,  extraction  of  the  soil  for  24  hours 
with  12  percent  cold  hydrochloric  acid  removes  all  of  the  inorganic 
phosphorus  readily  soluble  in  dilute  acids.  Would  not  such  treat- 
ment also  remove  any  inorganic  phosphorus  readily  soluble  in 
dilute  alkali?  It  would  certainly  seem  that  the  subsequent  extrac- 
tion with  dilute  ammonia  of  the  acid  extracted  residue  ought  to 
dissolve  only  organic  phosphorus.  This  idea  was  confirmed  by  ex- 
perimental evidence  and  thus  additional  information  regarding  the 
nature  of  the  ammonia-soluble  phosphorus  was  obtained. 

Two  samples  of  10  grams  each  of  the  soil  under  consideration 
were  extracted  for  24  hours  with  100  c.c  of  12  percent  cold  hydro- 
chloric acid,  then  filtered  and  washed  with  hot  water  until  the  fil- 
trate was  free  from  chlorides.  One  of  the  samples  was  then 
extracted  with  4  percent  ammonia  for  36  hours  in  the  usual  way 
and  the  amount  of  ammonia-soluble  phosphorus  determined :  the 
second  sample  was  again  extracted  with  12  percent  cold  hydro- 
chloric acid  for  36  hours  and  the  amount  of  soluble  phosphorus 
determined.  Both  experiments  were  duplicated.  The  dilute  am- 
monia extracted  540  and  570  pounds  of  phosphorus  or  an  average 
of  555  pounds  of  phosphorus  per  two  million  pounds  of  soil  which 
had  previously  been  extracted  with  cold  12  percent  hydrochloric 
acid,  while  a  second  extraction  with  cold  12  percent  hydrochloric 
acid  yielded  only  94  and  96  pounds  or  an  average  of  95  pounds  of 
phosphorus  per  two  million  pounds  of  soil. 

It  would  seem  reasonable  to  suppose  that  both  extractions  of 
the  soil  with  cold  12  percent  hydrochloric  acid  removed  some 
organic  phosphorus  since  Berthelot  and  Andre  (31)  have  demon- 
strated that  organic  matter  of  the  soil  is  somewhat  soluble  in  this 
reagent. 

It  would  also  seem  very  unreasonable  to  suppose  that  dilute 
ammonia  possessed  as  great  a  solvent  power  for  inorganic  phos- 
phorus as  does  12  percent  cold  hydrochloric  acid.  But,  assuming, 
for  the  sake  of  argument,  that  only  inorganic  phosphorus  is  ex- 
tracted by  the  hydrochloric  acid  and  that  dilute  ammonia  has  as 
great  a  solvent  power  for  inorganic  phosphorus  as  the  hydrochloric 
acid,  the  above  experiments  seem  to  demonstrate  that  at  least 
460  pounds  of  phosphorus  (555-95)  of  the  ammonia-soluble  phos- 
phorus has  been  derived  from  organic  sources  and  that  at  least 
83  percent  of  the  ammonia- soluble  phosphorus  has  been  derived 
from  organic  sources. 


CARBON,  PHOSPHORUS  AND  NITROGEN  IN  SOILS  119 

(c)      ORGANIC    PHOSPHORUS    BY    SCHMOEGER^S    METHOD 

The  second  method  for  determining'  the  organic  phosphorus  is 
the  one  proposed  by  Schmoeger.  Eggert,  Nilson,  Tache  and  others 
have  shown  that  simple  ignition  increased  the  solubility  of  the 
phosphorus  in  cold  hydrochloric  acid.  The  increased  solubility  of 
the  phosphorus  was  believed  to  be  due  to  the  destruction  of  the 
organic  phosphorus  compounds.  Therefore,  the  amount  of  phos- 
phorus in  the  original  soil,  soluble  in  cold  hydrochloric  acid,  sub- 
tracted from  the  amount  in  the  ignited  soil  soluble  in  cold 
hydrochloric  acid  of  the  same  strength  was  regarded  as  having 
been  derived  from  the  organic  phosphorus  compounds.  This  as- 
sumption was  confirmed  by  Schmoeger  by  hydrolyzing  the  soil  un- 
der pressure  at  a  temperature  of  i4O°-i6o°C.  This  treatment  of 
the  soil  decomposed  the  organic  phosphorus  compounds  so  that  the 
organic  phosphorus  was  rendered  soluble  in  cold  hydrochloric  acid. 
The  difference,  therefore,  between  the  amount  of  phosphorus  ex- 
tracted from  the  original  soil  by  cold  hydrochloric  acid  and  the 
amount  extracted  from  the  soil  which  had  been  hydrolized  gave  the 
amount  of  organic  phosphorus.  Schmoeger  found  that,  as  a  rule, 
concordant  results  were  obtained  by  the  two  methods  altho  in  cer- 
tain cases  slightly  higher  results  were  obtained  by  the  latter  method. 

It  was  decided  to  determine  the  organic  phosphorus  by  both  of 
the  above  methods.  Thus,  10  grams  of  the  original  soil  was 
treated  with  100  c.c.  of  12  percent  hydrochloric  acid  and  digested 
in  the  cold  with  an  occasional  shaking  for  24  hours.  A  second 
sample  of  10  grams  was  ignited  and  then  extracted  with  12  percent 
cold  hydrochloric  acid  in  a  similar  manner.  At  the  end  of  24  hours 
the  extract  was  diluted  with  water  and  separated  by  filtration.  The 
residue  was  washed  with  cold  water  until  the  filtrate  was  free  from 
chlorides:  the  filtrate  was  then  made  up  to  500  c.c.  and  100  c.c. 
used  for  the  phosphorus  determination.  The  results  recorded  in 
Table  24  show  that  there  are  271  pounds  of  phosphorus  in  the 
original  soil  soluble  in  12  percent  cold  hydrochloric  acid  while 
there  are  814  pounds  in  the  ignited  soil  soluble  in  the  same  reagent. 
These  results  show,  therefore,  that  there  are  543  pounds  of  organic 
phosphorus  in  two  million  pounds  of  the  surface  soil. 

Another  sample  of  10  grams  of  the  soil  was  treated  with  acidu- 
lated water  and  heated  in  an  autoclave  for  12  hours  at  a  tempera- 
ture of  1 40°- 1 45 °C.  The  sample  was  then  digested  for  24  hours 
with  cold  hydrochloric  acid,  filtered  and  the  filtrate  made  up  to 
500  c.c.  An  average  of  two  determinations  show  that  878  pounds 
of  phosphorus  were  obtained.  This  would  indicate  that  there  were 
607  pounds  of  organic  phosphorus  in  two  million  pounds  of  the 
surface  soil.  Slightly  higher  results  for  organic  phosphorus  are  thus 


120 


BULLETIN  No.  145 


(April, 


obtained  by  the  autoclave  method  but  it  is  probably  more  nearly 
correct  since  it  is  difficult  to  conceive  how  the  treatment  in  the 
autoclave  would  render  any  inorganic  phosphorus  soluble  which 
would  not  be  rendered  soluble  by  ignition  while  the  work  of  Leav- 
itt  and  LeClerc  (81,  82)  would  indicate  that  ignition  might  render 
some  of  the  organic  phosphorus  insoluble  in  cold  hydrochloric  acid 
of  any  strength. 

The  calculation  method  shows  that  423  pounds  of  phosphorus 
per  two  millions  of  the  surface  soil  are  in  organic  combination: 
the  ammoniacal  extraction  method  shows  504  pounds  of  organic 
phosphorus  and  the  ignition  method  shows  543  pounds,  while 

TABLE  24.— PHOSPHORUS  SOLUBLE  IN  TWELVE  PERCENT  HYDROCHLORIC  ACID: 
RESULTS  EXPRESSED  AS  POUNDS  IN  Two  MILLION  POUNDS  OF  SOIL 


Number 

A 
B 

Original 
soil 

Ignited 
soil 

Organic 
phosphorus 

266 
276 

819 
809 

Average 

271 

814 

543 

TABLE  25. — PHOSPHORUS  SOLUBLE  IN  TWELVE  PERCENT  HYDROCHLORIC  ACID: 
RESULTS  EXPRESSED  AS  POUNDS  IN  Two  MILLION  POUNDS  OF  SOIL 


Number 

Original 
soil 

Evaporated 
soil 

Organic 
phosphorus 

A 

B 

266 
276 

876 
880 

Average 

271 

878 

607 

Schmoeger's  method  shows  that  there  are  607  pounds  of  organic 
phosphorus.  The  calculation  method  is,  therefore,  very  conserva- 
tive in  nature  and  it  can  be  safely  stated  that  at  least  that  much 
phosphorus  is  in  organic  combination.  Table  26  gives  the  sum- 
marized results  of  the  organic  phosphorus  obtained  by  the  several 
methods. 


TABLE  26. — TOTAL  PHOSPHORUS  AND  ORGANIC  PHOSPHORUS  BY  SEVERAL 

METHODS 


Organic  phos- 
phorus by  cal- 
culation 

Organic  phos- 
phorus by  solu- 
tion in  dilute 
ammonia 

Organic  phos- 
phorus by  ig- 
nition 

Organic  phos- 
phorus by  evap- 
oration 
(Schmoeger) 

Total 
phos- 
phorus 

Pounds 
per  two 
million 
pounds 
of  soil 

Per- 
cent of 
total 

Pounds 
per  two 
million 
pounds 
of  soil 

Per- 
cent of 
total 

Pounds 
per  two 
million 
pounds 
of  soil 

Per- 
cent of 
total 

Pounds 
per  two 
million 
pounds 
of  soil 

Per- 
cent of 
total 

919 

423             46 

504             55 

543             60 

607             66 

jp/o]  CARBON,  PHOSPHORUS  AND  NITROGEN  IN  SOILS  121 


CONCLUSIONS 

1.  The  phosphorus-nitrogen  ratio  in  the  surface  soil  of  the 
brown  silt  loam  soils  is  I  113.5  while  the  same  ratio  in  the  black 
clay  loam  soils  is  i  111.4. 

2.  Under  normal  conditions  the  nitrogen-carbon  ratio  of  the 
soil  has  a  tendency  to  become  narrower  as  the  age  of  the  organic 
material  increases :   the  ratio,  however,  never  becomes  narrower  or 
even  equal  to  the  ratio  of  the  more  common  proteins  contained  in 
the  humus  producing  materials. 

3.  The  nitrogen-carbon  ratios  of  the  ordinary  brown  silt  loam 
soils  of  Illinois  are  1:12.1,   1:11.5  and  1:8.9  m  tne  surface,  sub- 
surface, and  subsoil  respectively. 

The  ratios  in  the  black,  clay  loam  soils  are    1 111.7,  1 111.9  and 
i  :Q  in  the  surface,  subsurface,  and  subsoil  respectively. 

4.  The    phosphorus-carbon  ratio    in  the  surface    soil  of    the 
brown  silt  loam  is  i  :i65.2  while  the  ratio  in  the  surface  soil  of  the 
black  clay  loam  soils  is  1 1163.6. 

5.  1^  calculation  method  for  determining  organic  phosphorus 
is  very  cwiservative  in  character  and  can  be  relied  upon  in  drawing 
broad  general  conclusions. 

6.  The  evaporation  on  the  water  bath  of  the  ammoniacal  so- 
lution, in  the  preparation  of  the  mailer e  noire  in  quantity  for  analy- 
sis, causes  a  hydrolysis  of  the  organic  phosphorus  compounds. 

7.  The  determination  of  the  phosphorus  associated  with  the 
precipitated  matiere  noire  is  not  a  quantitative  method  for  the  de- 
termination of  the  total  organic  phosphorus  of  the  soil.      It  should 
be  regarded  only  as  a  good  qualitative  evidence  of  the  existence  of 
organic  phosphorus  in  the  soil. 

8.  The  contention  of  Fraps  that,  "There  is  no  evidence  that 
the  phosphoric  acid  in  the  nitrate  is  in  organic  combination"  and 
that,  "It  is"  probably  derived  from  the  iron  and  aluminium  phos- 
phates" is  entirely  untenable. 


/p/o]  CARBON,  PHOSPHORUS  AND  NITROGEN  IN  SOILS  123 


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